1. Field of the Invention
The present invention relates to high-frequency signal transmission lines and electronic devices, more particularly to high-frequency signal transmission lines for transmission of high-frequency signals and electronic devices.
2. Description of the Related Art
One of known examples of an invention relating to the conventional high-frequency signal transmission lines is a high-frequency signal line disclosed in WO 2012/073591. This high-frequency signal line includes a dielectric element assembly, a signal line, two ground conductors, and via-hole conductors. The dielectric element assembly is formed by laminating a plurality of dielectric sheets. The signal line is provided inside the dielectric element assembly. The signal line is provided between the two ground conductors in terms of the direction of the lamination in the dielectric element assembly. The via-hole conductors pierce through the dielectric sheets in the direction of the lamination and connect together the two ground conductors. The two via-hole conductors are arranged along the width direction of the dielectric element assembly such that the signal line is provided between the via-hole conductors in the dielectric element assembly. With this arrangement, the signal line and the two ground conductors form a stripline structure.
Further, the ground conductors have a plurality of openings which overlap with the signal line when viewed in plan in the direction of the lamination. With this arrangement, capacitance is unlikely to be formed between the signal line and the ground conductors. Therefore, the distance in the direction of the lamination between the signal line and the ground conductors can be reduced, and the thickness of the high-frequency signal line can also be reduced. The high-frequency signal line having such a configuration is used for connection of two circuit boards.
The high-frequency signal line disclosed in WO 2012/073591 has difficulty in reducing the width of the dielectric element assembly as described below. More specifically, in the high-frequency signal line disclosed in WO 2012/073591, reduction of the width of the dielectric element assembly may be realized by, for example, reducing the diameter of the via-hole conductors. However, the minimum value of the diameter of the via-hole conductors is limited by the accuracy of the manufacturing process of the via-hole conductors. Therefore, there is a limitation in reducing the width of the dielectric element assembly by reducing the diameter of the via-hole conductors.
Reduction of the width of the dielectric element assembly may also be realized by, for example, reducing the width of the signal line. However, when the width of the signal line is reduced, the resistance value of the signal line increases, and the insertion loss of the high-frequency signal line also increases.